Radio spectrum is a limited resource in wireless networks. Therefore, intense efforts are made to use the available spectrum as efficiently as possible. With increasing demands for data communication and high bit rates this will become even more important in the future.
Typically different parts of the radio spectrum are licensed out to operators who build communications systems utilizing the relevant parts. These systems may be seen as the primary systems in each respective part of the radio spectrum.
When a piece of licensed radio spectrum is not used for a period of time for its primary purpose in a certain geographical network, for example, for wide area cellular communication, there will be a desire to use it for other purposes.
A potentially important use could be short range peer-to-peer communication, that is, direct communication without the use of intermediary nodes such as base stations, between the user terminals used in the primary communication system of the licensed spectrum.
A typical use of peer-to-peer communication could be over short distances, for example, for communication between one person's cellphone and laptop, or between two laptops on the same desk. Short distance means that a rather low transmit power is sufficient and hence that a single radio resource (frequency, time slot) that is not used for the primary system can be re-used for many simultaneous peer-to-peer communication sessions in physically separated places. Hence, a higher total throughput can be obtained within the given spectrum, compared to communicating through the primary system. This type of peer-to-peer communication can also be seen as a natural part of an “always best connected” concept, that is, to ensure that the type of connection utilizing the network resources in the most efficient way at any given time is always selected.
However, since peer-to-peer communication would take place in a licensed spectrum, network operators may be expected to require control of radio resources and the interference in the network. Prior art solutions for peer-to-peer communication do not account for this need.
The TETRA (Terrestrial Trunked Radio) concept provides a Managed Direct Mode (MDMO), described in the ETSI standard EN300396-10: “Managed Direct Mode Operation (M-DMO) enables the use of DMO to be controlled by providing a mechanism by which frequencies may be given for DMO use for a period of time. The objective of M-DMO is to constrain the transmission by the M-DMO terminals such that they will not transmit in a geographical area in which they are not authorized to transmit”. The direct transmission between terminals is restricted by a broadcast signal indicating which mobile terminals are allowed to use the direct mode. There are no restrictions based on the actual effect of the peer-to-peer communication on the network.